// Package parser provides sequence diagram parsing based on sequenceDiagram.jison
package parser

import (
	"fmt"
	"strings"

	"mermaid-go/pkg/ast"
	"mermaid-go/pkg/lexer"
)

// SequenceParser implements sequence diagram parsing following sequenceDiagram.jison
type SequenceParser struct {
	tokens  []lexer.Token
	current int
	diagram *ast.SequenceDiagram
	// messageCollector allows routing parsed messages into current container (loop/alt/opt/par)
	messageCollector func(msg *ast.SequenceMessage)
}

// NewSequenceParser creates a new sequence parser
func NewSequenceParser() *SequenceParser {
	return &SequenceParser{
		diagram: ast.NewSequenceDiagram(),
	}
}

// Parse parses sequence diagram syntax
func (p *SequenceParser) Parse(input string) (*ast.SequenceDiagram, error) {
	// Tokenize
	l := lexer.NewLexer(input)
	tokens, err := l.Tokenize()
	if err != nil {
		return nil, fmt.Errorf("lexical analysis failed: %w", err)
	}

	// Filter tokens
	p.tokens = lexer.FilterTokens(tokens)
	p.current = 0
	p.diagram = ast.NewSequenceDiagram()
	p.messageCollector = func(msg *ast.SequenceMessage) {
		p.diagram.Messages = append(p.diagram.Messages, msg)
	}

	// Parse document
	err = p.parseDocument()
	if err != nil {
		return nil, fmt.Errorf("syntax analysis failed: %w", err)
	}

	return p.diagram, nil
}

// parseDocument parses the sequence diagram document
func (p *SequenceParser) parseDocument() error {
	// Expect sequenceDiagram
	if !p.check(lexer.TokenID) || p.peek().Value != "sequenceDiagram" {
		return p.error("expected 'sequenceDiagram'")
	}
	p.advance()

	// Parse statements
	for !p.isAtEnd() {
		if err := p.parseStatement(); err != nil {
			return err
		}
	}

	return nil
}

// parseStatement parses individual sequence diagram statements
func (p *SequenceParser) parseStatement() error {
	if p.isAtEnd() {
		return nil
	}

	token := p.peek()
	switch {
	case p.check(lexer.TokenNewline):
		p.advance() // Skip newlines
		return nil
	case p.checkKeyword("participant"):
		return p.parseParticipant()
	case p.checkKeyword("actor"):
		return p.parseActor()
	case p.checkKeyword("Note"):
		return p.parseNote()
	case p.checkKeyword("loop"):
		return p.parseLoop()
	case p.checkKeyword("alt"):
		return p.parseAlt()
	case p.checkKeyword("opt"):
		return p.parseOpt()
	case p.checkKeyword("par"):
		return p.parsePar()
	case p.checkKeyword("box"):
		return p.parseBox()
	case p.checkKeyword("rect"):
		return p.parseRect()
	case p.checkKeyword("critical"):
		return p.parseCritical()
	case p.checkKeyword("option"):
		_, err := p.parseOption()
		return err
	case p.checkKeyword("break"):
		return p.parseBreak()
	case p.checkKeyword("activate"):
		return p.parseActivate()
	case p.checkKeyword("deactivate"):
		return p.parseDeactivate()
	case p.check(lexer.TokenID):
		// Try to parse as message
		return p.parseMessage()
	default:
		return p.error(fmt.Sprintf("unexpected token: %s", token.Value))
	}
}

// parseParticipant parses participant statements
func (p *SequenceParser) parseParticipant() error {
	p.advance() // consume 'participant'

	if !p.check(lexer.TokenID) {
		return p.error("expected participant ID")
	}

	id := p.advance().Value
	participant := &ast.SequenceParticipant{
		ID:   id,
		Name: id,
		Type: ast.ParticipantTypeParticipant,
	}

	// Check for 'as' alias
	if p.checkKeyword("as") {
		p.advance() // consume 'as'
		if !p.check(lexer.TokenID) && !p.check(lexer.TokenString) {
			return p.error("expected participant name after 'as'")
		}
		name := p.advance().Value
		if strings.HasPrefix(name, "\"") && strings.HasSuffix(name, "\"") {
			name = name[1 : len(name)-1] // Remove quotes
		}
		participant.Name = name
	}

	p.diagram.Participants = append(p.diagram.Participants, participant)
	return nil
}

// parseActor parses actor statements (similar to participant but different type)
func (p *SequenceParser) parseActor() error {
	p.advance() // consume 'actor'

	if !p.check(lexer.TokenID) {
		return p.error("expected actor ID")
	}

	id := p.advance().Value
	participant := &ast.SequenceParticipant{
		ID:   id,
		Name: id,
		Type: ast.ParticipantTypeActor,
	}

	// Check for 'as' alias
	if p.checkKeyword("as") {
		p.advance() // consume 'as'
		if !p.check(lexer.TokenID) && !p.check(lexer.TokenString) {
			return p.error("expected actor name after 'as'")
		}
		name := p.advance().Value
		if strings.HasPrefix(name, "\"") && strings.HasSuffix(name, "\"") {
			name = name[1 : len(name)-1] // Remove quotes
		}
		participant.Name = name
	}

	p.diagram.Participants = append(p.diagram.Participants, participant)
	return nil
}

// parseMessage parses sequence diagram messages
func (p *SequenceParser) parseMessage() error {
	// Parse: FROM ARROW TO : MESSAGE
	from := p.advance().Value

	// Parse arrow type
	msgType, err := p.parseArrowType()
	if err != nil {
		return err
	}

	if !p.check(lexer.TokenID) {
		return p.error("expected target participant")
	}
	to := p.advance().Value

	var message string
	if p.check(lexer.TokenColon) {
		p.advance() // consume ':'
		// Collect message text until newline
		var msgParts []string
		for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
			msgParts = append(msgParts, p.advance().Value)
		}
		message = strings.TrimSpace(strings.Join(msgParts, " "))
	}

	seqMsg := &ast.SequenceMessage{
		From:    from,
		To:      to,
		Message: message,
		Type:    msgType,
	}

	// Route message to current collector (global or container)
	if p.messageCollector != nil {
		p.messageCollector(seqMsg)
	} else {
		p.diagram.Messages = append(p.diagram.Messages, seqMsg)
	}

	// Ensure participants exist
	p.ensureParticipant(from)
	p.ensureParticipant(to)

	return nil
}

// parseArrowType parses arrow types for messages
func (p *SequenceParser) parseArrowType() (ast.SequenceMessageType, error) {
	token := p.peek()

	// Handle different arrow token types from lexer
	switch token.Type {
	case lexer.TokenArrowSolid:
		p.advance()
		return ast.MessageTypeSolid, nil
	case lexer.TokenArrowDotted:
		p.advance()
		return ast.MessageTypeDotted, nil
	case lexer.TokenArrowCross:
		p.advance()
		return ast.MessageTypeSolidCross, nil
	case lexer.TokenArrowOpen:
		p.advance()
		return ast.MessageTypeSolidOpen, nil
	default:
		// Fallback for unrecognized arrow patterns
		if token.Value == "-->" {
			p.advance()
			return ast.MessageTypeDotted, nil
		} else if token.Value == "->" {
			p.advance()
			return ast.MessageTypeSolid, nil
		} else if token.Value == "-x" {
			p.advance()
			return ast.MessageTypeSolidCross, nil
		} else if token.Value == "-->x" || token.Value == "--x" {
			p.advance()
			return ast.MessageTypeDottedCross, nil
		} else if token.Value == "-)" {
			p.advance()
			return ast.MessageTypeSolidOpen, nil
		} else if token.Value == "--)" {
			p.advance()
			return ast.MessageTypeDottedOpen, nil
		} else if token.Value == "<->" {
			p.advance()
			return ast.MessageTypeBidirectional, nil
		}
	}

	return "", p.error("expected arrow type")
}

// parseNote parses note statements
func (p *SequenceParser) parseNote() error {
	p.advance() // consume 'Note'

	var placement ast.NotePlace
	var actor string

	if p.checkKeyword("left") {
		p.advance()
		if !p.checkKeyword("of") {
			return p.error("expected 'of' after 'left'")
		}
		p.advance()
		placement = ast.NotePlaceLeft
	} else if p.checkKeyword("right") {
		p.advance()
		if !p.checkKeyword("of") {
			return p.error("expected 'of' after 'right'")
		}
		p.advance()
		placement = ast.NotePlaceRight
	} else if p.checkKeyword("over") {
		p.advance()
		placement = ast.NotePlaceOver
	} else {
		return p.error("expected note placement (left of, right of, over)")
	}

	if !p.check(lexer.TokenID) {
		return p.error("expected participant ID for note")
	}
	actor = p.advance().Value

	if !p.check(lexer.TokenColon) {
		return p.error("expected ':' after participant in note")
	}
	p.advance()

	// Collect note text
	var noteParts []string
	for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
		noteParts = append(noteParts, p.advance().Value)
	}
	noteText := strings.TrimSpace(strings.Join(noteParts, " "))

	note := &ast.SequenceNote{
		Actor:     actor,
		Placement: placement,
		Message:   noteText,
	}

	p.diagram.Notes = append(p.diagram.Notes, note)
	return nil
}

// Placeholder implementations for complex structures
func (p *SequenceParser) parseLoop() error {
	p.advance() // consume 'loop'

	// Parse loop condition/label
	var labelParts []string
	for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
		labelParts = append(labelParts, p.advance().Value)
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	if p.check(lexer.TokenNewline) {
		p.advance()
	}

	loop := &ast.SequenceLoop{
		Label:    label,
		Messages: make([]*ast.SequenceMessage, 0),
	}

	// Temporarily redirect messages into loop
	prev := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) { loop.Messages = append(loop.Messages, msg) }

	// Parse statements until 'end'
	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prev
			return err
		}
	}
	p.messageCollector = prev

	p.diagram.Loops = append(p.diagram.Loops, loop)
	return nil
}

func (p *SequenceParser) parseAlt() error {
	p.advance() // consume 'alt'

	// Parse alt condition/label
	var labelParts []string
	for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
		labelParts = append(labelParts, p.advance().Value)
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	if p.check(lexer.TokenNewline) {
		p.advance()
	}

	alt := &ast.SequenceAlt{
		Label:        label,
		IfMessages:   make([]*ast.SequenceMessage, 0),
		ElseMessages: make([]*ast.SequenceMessage, 0),
	}

	// First phase: IF block
	prev := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) { alt.IfMessages = append(alt.IfMessages, msg) }
	for !p.isAtEnd() {
		if p.checkKeyword("else") {
			p.advance()
			if p.check(lexer.TokenNewline) {
				p.advance()
			}
			break
		}
		if p.checkKeyword("end") {
			p.advance()
			p.messageCollector = prev
			p.diagram.Alts = append(p.diagram.Alts, alt)
			return nil
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prev
			return err
		}
	}
	// Second phase: ELSE block
	p.messageCollector = func(msg *ast.SequenceMessage) { alt.ElseMessages = append(alt.ElseMessages, msg) }
	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prev
			return err
		}
	}
	p.messageCollector = prev

	p.diagram.Alts = append(p.diagram.Alts, alt)
	return nil
}

func (p *SequenceParser) parseOpt() error {
	p.advance() // consume 'opt'

	// Parse opt condition/label
	var labelParts []string
	for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
		labelParts = append(labelParts, p.advance().Value)
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	if p.check(lexer.TokenNewline) {
		p.advance()
	}

	opt := &ast.SequenceOpt{
		Label:    label,
		Messages: make([]*ast.SequenceMessage, 0),
	}

	prev := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) { opt.Messages = append(opt.Messages, msg) }

	// Parse statements until 'end'
	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prev
			return err
		}
	}

	p.messageCollector = prev
	p.diagram.Opts = append(p.diagram.Opts, opt)
	return nil
}

func (p *SequenceParser) parsePar() error {
	p.advance() // consume 'par'

	// Parse first section (no label)
	if p.check(lexer.TokenNewline) {
		p.advance()
	}

	par := &ast.SequencePar{
		Sections: make([]ast.SequenceParSection, 0),
	}

	currentSection := ast.SequenceParSection{
		Messages: make([]*ast.SequenceMessage, 0),
	}

	prev := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) { currentSection.Messages = append(currentSection.Messages, msg) }

	// Parse statements until 'and' or 'end'
	for !p.isAtEnd() {
		if p.checkKeyword("and") {
			// Save current section and start new one
			par.Sections = append(par.Sections, currentSection)
			p.advance() // consume 'and'

			// Parse label for new section
			var labelParts []string
			for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
				labelParts = append(labelParts, p.advance().Value)
			}
			label := strings.TrimSpace(strings.Join(labelParts, " "))

			currentSection = ast.SequenceParSection{
				Label:    &label,
				Messages: make([]*ast.SequenceMessage, 0),
			}
			// redirect collector to new section
			p.messageCollector = func(msg *ast.SequenceMessage) { currentSection.Messages = append(currentSection.Messages, msg) }

			if p.check(lexer.TokenNewline) {
				p.advance()
			}
			continue
		}
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prev
			return err
		}
	}

	// Add final section
	par.Sections = append(par.Sections, currentSection)
	p.messageCollector = prev
	p.diagram.Pars = append(p.diagram.Pars, par)
	return nil
}

func (p *SequenceParser) parseBox() error {
	p.advance() // consume 'box'

	var name string
	var color *string

	// Parse box name and optional color
	if p.check(lexer.TokenString) {
		name = p.advance().Value
		// Remove quotes
		if strings.HasPrefix(name, "\"") && strings.HasSuffix(name, "\"") {
			name = name[1 : len(name)-1]
		}
	} else if p.check(lexer.TokenID) {
		name = p.advance().Value
	}

	// Check for color
	if p.check(lexer.TokenID) {
		colorVal := p.advance().Value
		color = &colorVal
	}

	box := &ast.SequenceBox{
		Name:         name,
		Color:        color,
		Participants: make([]string, 0),
	}

	// Parse participants until 'end'
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		if p.check(lexer.TokenID) {
			participant := p.advance().Value
			box.Participants = append(box.Participants, participant)
		} else {
			break
		}
	}

	p.diagram.Boxes = append(p.diagram.Boxes, box)
	return nil
}

// parseRect parses 'rect ... end' blocks
func (p *SequenceParser) parseRect() error {
	p.advance() // consume 'rect'

	var color *string
	// Parse optional color (collect all tokens until newline)
	var colorParts []string
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		token := p.advance()
		colorParts = append(colorParts, token.Value)
	}

	if len(colorParts) > 0 {
		colorVal := strings.Join(colorParts, "")
		color = &colorVal
	}
	if p.check(lexer.TokenNewline) {
		p.advance()
	}

	rect := &ast.SequenceRect{
		Color:    color,
		Messages: make([]*ast.SequenceMessage, 0),
	}

	// Set up message collector for this rect
	prevCollector := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) {
		rect.Messages = append(rect.Messages, msg)
	}

	// Parse inner statements until 'end'
	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prevCollector
			return err
		}
	}

	// Restore previous collector
	p.messageCollector = prevCollector
	p.diagram.Rects = append(p.diagram.Rects, rect)
	return nil
}

// parseCritical parses 'critical ... option ... end' blocks
func (p *SequenceParser) parseCritical() error {
	p.advance() // consume 'critical'

	// Parse label (rest of line)
	var labelParts []string
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		labelParts = append(labelParts, p.advance().Value)
	}
	if p.check(lexer.TokenNewline) {
		p.advance()
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	critical := &ast.SequenceCritical{
		Label:    label,
		Options:  make([]*ast.SequenceOption, 0),
		Messages: make([]*ast.SequenceMessage, 0),
	}

	// Set up message collector for this critical
	prevCollector := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) {
		critical.Messages = append(critical.Messages, msg)
	}

	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if p.checkKeyword("option") { // allow options sections
			option, err := p.parseOption()
			if err != nil {
				p.messageCollector = prevCollector
				return err
			}
			critical.Options = append(critical.Options, option)
			continue
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prevCollector
			return err
		}
	}

	// Restore previous collector
	p.messageCollector = prevCollector
	p.diagram.Criticals = append(p.diagram.Criticals, critical)
	return nil
}

// parseOption parses an 'option ...' section within critical
func (p *SequenceParser) parseOption() (*ast.SequenceOption, error) {
	p.advance() // consume 'option'

	// Parse label (rest of line)
	var labelParts []string
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		labelParts = append(labelParts, p.advance().Value)
	}
	if p.check(lexer.TokenNewline) {
		p.advance()
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	option := &ast.SequenceOption{
		Label:    label,
		Messages: make([]*ast.SequenceMessage, 0),
	}

	// Set up message collector for this option
	prevCollector := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) {
		option.Messages = append(option.Messages, msg)
	}

	// parse statements until next 'option' or 'end'
	for !p.isAtEnd() {
		if p.checkKeyword("option") || p.checkKeyword("end") {
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prevCollector
			return nil, err
		}
	}

	// Restore previous collector
	p.messageCollector = prevCollector
	return option, nil
}

// parseBreak parses 'break ... end' blocks
func (p *SequenceParser) parseBreak() error {
	p.advance() // consume 'break'

	// Parse label (rest of line)
	var labelParts []string
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		labelParts = append(labelParts, p.advance().Value)
	}
	if p.check(lexer.TokenNewline) {
		p.advance()
	}
	label := strings.TrimSpace(strings.Join(labelParts, " "))

	breakBlock := &ast.SequenceBreak{
		Label:    label,
		Messages: make([]*ast.SequenceMessage, 0),
	}

	// Set up message collector for this break
	prevCollector := p.messageCollector
	p.messageCollector = func(msg *ast.SequenceMessage) {
		breakBlock.Messages = append(breakBlock.Messages, msg)
	}

	for !p.isAtEnd() {
		if p.checkKeyword("end") {
			p.advance()
			break
		}
		if err := p.parseStatement(); err != nil {
			p.messageCollector = prevCollector
			return err
		}
	}

	// Restore previous collector
	p.messageCollector = prevCollector
	p.diagram.Breaks = append(p.diagram.Breaks, breakBlock)
	return nil
}

func (p *SequenceParser) parseActivate() error {
	p.advance() // consume 'activate'

	if !p.check(lexer.TokenID) {
		return p.error("expected participant ID after 'activate'")
	}

	actor := p.advance().Value

	activation := &ast.SequenceActivation{
		Actor: actor,
		Type:  ast.ActivationTypeActivate,
	}

	p.diagram.Activations = append(p.diagram.Activations, activation)
	return nil
}

func (p *SequenceParser) parseDeactivate() error {
	p.advance() // consume 'deactivate'

	if !p.check(lexer.TokenID) {
		return p.error("expected participant ID after 'deactivate'")
	}

	actor := p.advance().Value

	activation := &ast.SequenceActivation{
		Actor: actor,
		Type:  ast.ActivationTypeDeactivate,
	}

	p.diagram.Activations = append(p.diagram.Activations, activation)
	return nil
}

// ensureParticipant ensures a participant exists, creating it if needed
func (p *SequenceParser) ensureParticipant(id string) {
	for _, participant := range p.diagram.Participants {
		if participant.ID == id {
			return
		}
	}

	// Create participant if it doesn't exist
	participant := &ast.SequenceParticipant{
		ID:   id,
		Name: id,
		Type: ast.ParticipantTypeParticipant,
	}
	p.diagram.Participants = append(p.diagram.Participants, participant)
}

// Helper methods
func (p *SequenceParser) check(tokenType lexer.TokenType) bool {
	if p.isAtEnd() {
		return false
	}
	return p.peek().Type == tokenType
}

func (p *SequenceParser) checkNext(tokenType lexer.TokenType) bool {
	if p.current+1 >= len(p.tokens) {
		return false
	}
	return p.tokens[p.current+1].Type == tokenType
}

func (p *SequenceParser) checkKeyword(keyword string) bool {
	if p.isAtEnd() {
		return false
	}
	token := p.peek()

	// Handle special keywords that have their own token types
	switch keyword {
	case "end":
		return token.Type == lexer.TokenEnd
	default:
		return token.Type == lexer.TokenID && strings.EqualFold(token.Value, keyword)
	}
}

func (p *SequenceParser) advance() lexer.Token {
	if !p.isAtEnd() {
		p.current++
	}
	return p.previous()
}

func (p *SequenceParser) isAtEnd() bool {
	return p.current >= len(p.tokens) || p.peek().Type == lexer.TokenEOF
}

func (p *SequenceParser) peek() lexer.Token {
	if p.current >= len(p.tokens) {
		return lexer.Token{Type: lexer.TokenEOF}
	}
	return p.tokens[p.current]
}

func (p *SequenceParser) previous() lexer.Token {
	if p.current <= 0 {
		return lexer.Token{Type: lexer.TokenEOF}
	}
	return p.tokens[p.current-1]
}

func (p *SequenceParser) error(message string) error {
	token := p.peek()
	return fmt.Errorf("parse error at line %d, column %d: %s (got %s)",
		token.Line, token.Column, message, token.Type.String())
}

func (p *SequenceParser) skipToEnd(endKeyword string) error {
	for !p.isAtEnd() {
		if p.checkKeyword(endKeyword) {
			p.advance()
			break
		}
		p.advance()
	}
	return nil
}

func (p *SequenceParser) skipToNextStatement() error {
	for !p.isAtEnd() && !p.check(lexer.TokenNewline) {
		p.advance()
	}
	if p.check(lexer.TokenNewline) {
		p.advance()
	}
	return nil
}